We're doing something like that in Germany where some fines are calculated by how much you're making in a day, so you'd get "30 days' worth".
Unfortunately, they aren't actually looking a your assets and income, but make a guess and if it's too high, you can provide proof that it's not accurate. It's usually far too low when you're in the top 5%.
> Unfortunately, they aren't actually looking a your assets and income
Wisdom of the policy aside, why is it implemented in such a seemingly insane way? Why not just look at the equivalent of last year's W2? While not perfectly representative of steady-state income, it's what many other income-based systems do and you can easily have a petition process for claiming that that year's income is unrepresentative.
Mostly because of privacy laws. A court can't simply access tax documents, even if it might be helpful in this case. If they wanted to, they'd have to go the official route and the judge ruling on that would weigh the interest of the individual to keep his info private against the interest of the court to gain information. This obviously is easy when the documents are related to the crime, but as the crime/misdemeanor has already been decided upon and only the sentencing is to be done, privacy is usually given more weight.
Unfortunately, they aren't actually looking a your assets and income, but make a guess and if it's too high, you can provide proof that it's not accurate. It's usually far too low when you're in the top 5%.